Battery case with balsa wood?

[Pablo_1985]

Hi guys, the other day i saw here in the forum how a guy made a kayak with balsa wood, then paint it with epoxi, and it seems that it worked perfectly allright...so, now i´m going to change my electric kit to another bike for improving my actual bike, and i want to put my batteries in the frame, because now they are in a rear rack, and it is much better for weight distribution and so changing them to the frame.

I have a 48V 10Ah LIFEPO4 pack and i was thinking about disasbling it, taking the batteries and putting them in the frame in a custom box (with balsa wood) and fix it to the frame with some kind of hose clamps. ¿What do you think about this, somebody has tried to work with this kind of wood?? maybe it is too much weight for it, and i should reinforce it or something similar, but if can handle the vibration and weight and i can make a water proof, and good looking, pack...maybe i could put also the controller there with something for the air flow. At the end of this week i should have my new bike, i will post some pictures and sketches (with sketchup), and see what do you think.

this is the battery, and it is too big for being in the frame and pedalling at the same time...

http://picasaweb.google.com/lh/photo/8cptZ0jcc0HOBMX3yZkwCw?feat=directlink

http://picasaweb.google.com/lh/photo/NTZGTigG0jtMZ9Q30fPBBw?feat=directlink

Ideas are wellcome.

EDIT: I forget to say, i´m thinking about balsa because it is light and very easy to work with.
EDIT2: Anyone knows where can i find hose clamps to fix the box to the frame tubes?

 

[FMB42]

I'd use fiberglass myself.

 

[docnjoj]

Balsa should work if it is covered inside and out with glass/epoxy. Full size homebuilt aircraft are made this way. Maybe carbon reinforcement on the outside.
otherDoc

 

[texaspyro]

Maybe carbon reinforcement on the outside.

Many people don't realize that carbon fiber conducts electricity. Treat it like it is metal.

 

[MitchJi]

Hi,

Using Balsa is discussed at some length in this thread:
http://endless-sphere.com/forums/viewtopic.php?uid=6504&f=6&t=22612&start=0

I'd use these instead of hose clamps:
http://endless-sphere.com/forums/viewtopic.php?f=28&t=22089

 

[John in CR]

For a battery box, I'd go with 4mm plywood impregnated with epoxy and a layer of glass in a second interior coat of epoxy on the interior. Just epoxy as the top coat on the outside to keep finish work easy, since I'm not fond of fiberglass powder during sanding. You can't cut 4mm ply with a knife like balsa, but the multi-direction layers of plywood will be stronger than balsa in such a thin form. Balsa is strong and stiff, but it's weakness is impact resistance, so a battery box may not be the best use.

I'm taking advantage of balsa strength and stiffness to add rigidity to a thin steel frame, but my batteries will be enclosed within the steel skeleton with duct tape protecting the batteries and probably foam rubber to make the fit snug to prevent movement. I'll use 3mm ply between each layer of batteries, not balsa.

 

[lifepo4ever]

balsa is very fragile i do rc plane with that but i break easy so the best thing i found was lexan sheet , just cut and glue and after use white or black duck tape around it so it will not broke if you go ride in cold wheather.

 

[Pablo_1985]

Thank´s guys i will post some photos about the final result

 

[Pablo_1985]

Ok, guys i don´t need the balsa, y can use the ofset box, i didn´t expect to fix in to the frame, but it does !

See, here is my bike with a box simulating the battery, also i did a drawing with some measures

http://picasaweb.google.com/lh/photo/TixPnxxVSHBB7ZNYAFIJsg?feat=directlink

http://picasaweb.google.com/lh/photo/QK_AmkB0-1VKsfiZ_HNxng?feat=directlink

So, now i have to think about something to put the battery there... i have market the screws for the water bottle, maybe they can help me... The thing is that with just 15,7cm, i have to make a support wich doesn´t move at all, and doesn´t take lateral space because then it could crash with the cranks...

Ideas are welcome!

 

[John in CR]

Here's what I did using the water bottle bolt holes to fit a Ping pack in a triangle. It's just an L shaped piece of steel using 2 bolts on the seat tube and 1 on the downtube. I lined the steel with some 1/4" hard foam rubber and used bungies to hold the pack securely in place. I used a vise to flatten the top side of the downtube to get just the right fit for the pack, but otherwise it was just a direct bolt on once I cut the piece of metal, bent it to shape, and drilled the holes. That was 2.5 years ago and it hasn't budged. The black stuff is silicone caulk that I slathered on before bolting, I forget why I thought it was necessary.

 

[lifepo4ever]

i done the same for my ping battery but with one more bracket on the top bolted to the box so it fit with the tube offrame of the bike , it prevent to play if you fall and also for rougth road
pading is also very good like John use for vibration

 

[Pablo_1985]

Yeah, but the thing is i have to make something to avoid any lateral movement in order to keep the battery away of the crank. Also, Because "Spain is diferent", i have to make something to avoid people to take my battery out :S. Now i have a design in mind, but is is not thieft proof...

EDIT: Also it should me allow me to take aout the battery witout breaking anything!something to make it plug and play!

 

[Pablo_1985]

Ok, i was thinking about something like this:

http://picasaweb.google.com/lh/photo/yNxOE73bksIRQ-0LtF_dWQ?feat=directlink

Now maybe a metal strip from the upper screw of the vertical tube, to the other piece, up to the battery and closing it with a padlock or something similar... see

http://picasaweb.google.com/lh/photo/TaM1g7G_pOVMi00odCBF-g?feat=directlink

Regards

 

[Pablo_1985]

another option is dissasemble the batteries and make something similar to a sandwich with the batteries in the middle with polystyrene, with the covers in aluminium, all of this filling completly the main triangle of the frame. I will fix this structure to the frame with clamps... this is a harder option.... im not sure about what to do...

 

[Pablo_1985]

The last option is out of the question, each headway cell is too big for trying to make something much better than the first option, furthermore there is the BMS who is quite bigger and i can´t place it very good...

So let´s try with the first one!

 

[John in CR]

"Spain is different"- My only saving grace here is that the petty thieves don't have a clue as to the value of the batteries on my bikes. Thank goodness ebikes haven't really hit Costa Rica yet.

 

[auraslip]

Why clamps?

Most hardware stores sell metal straps for construction and repair. Easy to bend in a vise, and cheap.

 

[Pablo_1985]

John, you could have just a very bad and rusty seat, but if you don´t do anything to avoid thieves, they will take it... At least in the parking of my company i have cameras, and security

Thanks for the advise Auraslip, but at the end it doesn´t seem that i could need any clap

I will post with updates, but right now the bike is quite nice, the magura hs33 rocks!... maybe i will have problems with the true of the rear wheel, my spokes seems to be a little bit longer than they should...

Regards

 

[Pablo_1985]

I have been thinking about the design, and i get with a way of mounting batteries, controller and some thing more inside the main triangle of the frame, so i will do a fiber glass box for this (fisrt time i use fiber glass!). I know that i saw something here in the forum, a guy who did a grey box in the main triangle of the frame (i can´t find it!), it was perfect! and i should do something similar... i have to figure out a way to keep everything tight inside the box, make a door, or something wich allow me access to the batteries, find some clamps or something similar for fixing the box to the frame, some way of integrating the alarm (i have this one http://www.corporatetravelsafety.com/catalog/lock-alarm-with-foot-cable-p-261.html ), the turnigy watt meter...and finally putt all this stuff in just one design!

Regards!

 

[Pablo_1985]

This is what i should do
http://endless-sphere.com/forums/viewtopic.php?f=6&t=13411

Anyone could tell me how many fiber glass layers should i use? wich kind of fiber glass?

I was thinking about using this one:
http://www.feroca.com/productos_detalle_02.asp?co_producto=303

but i don´t know anything about the strength! :S so i don´t know how many layers should i put.

Regards

 

[lifepo4ever]

This is what i should do
http://endless-sphere.com/forums/viewtopic.php?f=6&t=13411

Anyone could tell me how many fiber glass layers should i use? wich kind of fiber glass?

I was thinking about using this one:
http://www.feroca.com/productos_detalle_02.asp?co_producto=303

but i don´t know anything about the strength! :S so i don´t know how many layers should i put.

Regards

its depend of what kind of fiberglass you buy some are thicker then other but if you on your local bodyshop stuff you will have all the stuff including resin and harder
and much cheaper for bigger quantity you buy i really like the design of the case I really think i will build want for my second battery pack but the only thing i want is a removable case with strap so if i need just one pack can remove and also for charging the pack inside the house and leave the bike outside winter time

2-3mm wall should be enougth so 2 layer of fine fiberglass or one layer of thick one but i will see when i will built one

DON'T FORGET TO USE EPOXY RESINE BECAUSE REGULAR RESIN WILL MELT THE FOAM

 

[Pablo_1985]

You can use regular resin if you isolate the foam, i have talk about this issue with some people and all of them agree that with just covering the foam with film plastic will be enough, easyer and cheaper

Thanks for the advice Lifepo, i hope having some time this week to buy the materials and start the job... this days ím working all the day.

 

[lifepo4ever]

You can use regular resin if you isolate the foam, i have talk about this issue with some people and all of them agree that with just covering the foam with film plastic will be enough, easyer and cheaper

Thanks for the advice Lifepo, i hope having some time this week to buy the materials and start the job... this days ím working all the day.

yes its also a good idea to cover it with something with some aluminium tape maybe but plastic will melt with the heat of the resine reaction built lot of heat

i will ask to my friend he a owner of a bodyshop

 

[Pablo_1985]

Oh thanks! if you can ask it would be great! I have already ask to a guy who usually do this things, he didn´t see any problem, but he never tryed also... so please ask!

Anyway the temperature of the resin can rise to 60ºC and if i make mixture little by little i don´t think that the block could rise to more than 50ºC (the mold and the fiber is cold, now is winter! hehehe), temperature that film can handle without problems and because i could find out wich is the fusion temperature of film plastic.

Regards!

 

[Pablo_1985]

Ok, i did some part of the job...but i could not use the foam mold, it was empty in the insede... instead i use a regular and cheaper (it was on the street) polypropyene.

I give it 2 layers on the side and 5 on the corners (300gr roving). This morning before i went to the work, i test a little... this thing is ultra strength!. SO when i come back from work i would start thinking about the door and the rest of things... at the end the box fitted on the frame just by hitting it :O

More photos
http://picasaweb.google.com/nuncaestardesillegaspronto/Venta?feat=directlink

Byt he way as you can see i use film plastic for the finishing... this think is incredible usefulll... i tried to make vacuumk but i need something like a foam to surround the piece and not sucking the plastic bag.. so i did this instead of vacuum (i also use it to isolate the polypropylene from the resin), it seems to work pretty well.

Regards!